Stereo systems for homes and especially for automobiles have become increasingly sophisticated in recent years to provide cleaner and sharper sound. The past several years have seen the development of compact discs and digital audio tape as part of an evolution of technology to provide better quality sound reproduction. The technology for speaker systems has also evolved to provide better quality sound transmission, even at high volumes. One problem that has received particular attention has been the problem of achieving good low frequency or bass response from speakers, especially at low end frequencies of 20-150 HZ. Poor response of low frequency or bass tones can cause popping or booming due to distortion of the sound at such low frequencies. This is especially a problem for automobile audio systems.
Formerly, speakers with large woofers were needed to provide high quality low frequency or bass tone response or reproduction. Attention has now been given to development of ported speaker enclosures such as bass reflex systems that are designed to enhance low frequency/bass response in speaker systems powered by relatively smaller speakers. Such ported speaker enclosures generally include a speaker cabinet in which a speaker is mounted. Baffles, folded tubes, or similar structures, are mounted within the speaker cabinet and define an audio transmission passageway therethrough. For example, U.S. Pat. Nos. 3,993,162 and 4,942,939 both disclose speaker enclosures having an enclosed cabinet with a series of interconnected tubes or baffles that define a labyrinthine passageway.
The principle behind such labyrinth enclosures is that as an airflow is generated within the speaker cabinet by the vibration of the speaker diaphragm, the airflow tends to bounce and move along the passageway defined by the tubes or baffles in a wave-like motion. Such movement causes the airflow to resinate at an increased rate as it moves along the audio passageway. The increased resonance of the airflow causes resonate peaks and provides an improved low frequency or bass tone response, even with smaller speakers. Variations on this concept are illustrated in U.S. Pat. Nos. 5,150,417, which discloses a speaker enclosure having a single substantially straight tube having series of openings formed along its length and covered by a membrane. U.S. Pat. No. 5,173,575 discloses a speaker enclosure having a relatively small cabinet having an externally extending resonance port that projects from a side of the speaker cabinet.
While such labyrinth type speaker enclosures have significantly improved the low frequency or bass response of conventional speaker systems, such systems are still subject to significant drawbacks. One major problem with such speaker enclosures is the size required for such enclosures. Prior art enclosures generally require large speaker cabinets which are bulky, heavy, and take up significant space, even though the speakers driving such systems are relatively small, in order to provide a sufficiently long audio passageway to enable enhanced resonance of the air flow within the enclosure. Such large cabinets are acceptable for use in a building or similar large structure, but take up too much space to be practical for installation in automobiles, especially in today's smaller compact cars. Such conventional speaker enclosures are also too large or bulky to be utilized in portable stereo systems or so called "bookshelf" systems.
Additionally, most conventional speaker enclosures are designed as an integral unit built around a specific speaker and thus cannot be adapted for use with other types of speakers and are often expensive to purchase and install. Further, conventional speaker enclosure assemblies are not tunable to fit the particular sound preferences of the listener. People hear sounds differently, and therefore some listeners may have a greater preference for a heavier bass, while other listeners will prefer greater treble. However, with most conventional speaker enclosure assemblies, the baffles or tubes of the assembly are fixedly mounted in an airtight cabinet and are therefore not tunable or adjustable so as to enable the tones produced by the enclosure to be tuned to fit the preference of the listener.
Accordingly, it can be seen that it would be desirable to provide a speaker enclosure assembly that enables enhanced low frequency or bass tone response to provide for improved sound quality, which assembly is extremely compact and which is tunable according to the preferences of the listener, and which is easily and inexpensively installed. It is to the provision of such a speaker enclosure assembly that the present invention is primarily directed.